Role of CD8+ CD25+ Foxp3+ regulatory T cells in multiple sclerosis

Objective The objective of this study was to investigate the role of CD8+ CD25+ FoxP3+ cells during the course of multiple sclerosis (MS). Methods Peripheral blood and cerebrospinal fluid (CSF) CD8+ T‐cell clones (TCCs) recognizing autoreactive CD4+ T cells were isolated from 20 MS patients during exacerbations, 15 patients in remission, 15 healthy subjects, and 10 patients with other inflammatory neurological diseases. Characteristics of noncytotoxic CD8+ CD25+ regulatory T cells were studied. Cell phenotype was evaluated using flow cytometry. Cytokine production and phospho‐signal transducer and activator of transcription 3 (STAT3) concentration were determined using enzyme‐linked immunosorbent assay. To assess 2,3‐dioxygenase (IDO) activity on dendritic cells (DCs), kynurenine concentration was measured by high‐performance liquid chromatography. Results Inhibition of CD4+ self‐reactive T‐cell proliferation, and of interferon‐γ and interleukin (IL)‐17 secretion, was observed after adding CD8+ CD25+ FoxP3+ cells to cultures. Suppression was abrogated by silencing FoxP3 using small interfering RNA. Cells were CD122+, CTLA‐4+, GITR+, CCR7+, and CD62L+, producing IL‐10 and transforming growth factor‐β. CD8+ CD25+ FoxP3+ cells downregulated costimulatory molecule expression on dendritic cells through a STAT3‐mediated pathway, resulting in less efficient antigen presentation, and induced IDO expression on DCs through STAT3 and cytotoxic T‐lymphocyte antigen 4‐dependent mechanisms. CD8+ regulatory TCC cloning frequency studied in blood and CSF was suppressed to a greater degree during exacerbations than during remission or in controls. Likewise, in CSF of MS patients during acute exacerbations, lower levels of CD8+ CD25+ FoxP3+ T cells were detected using flow cytometry. Interpretation CD8+ CD25+ FoxP3+ cells are novel regulatory cells exerting significant influence over self‐reactive CD4+ T‐cell regulation during the course of MS. Induction of these cells may provide new therapeutic alternatives for MS by eliminating or inhibiting self‐reactive T cells. ANN NEUROL 2010;67:625–638